Resistive device



June 18, 1946. F. H. BULLINGER 'RESISTIVE DEVICE Filed Sept. 4, 194a I NV EN TOR. fkmffi/a A! 5014/55/1".

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Patented June 18, 1946 7 RESISTIVE DEVICE Frederic H. Bullinger,Bronxvllle, N. Y., assignor to Ward Leonard Electric Company, acorporation of New York Application September 4, 1943, Serial No.501,213

Claims.

This invention relates to resistive devices, such as tubular resistiveunits wherein a resistive conductor is wound on an insulating tube andcovered with an insulating coating, such as vitreous enamel. andprovided with terminal connections.

In the devices of this type it is desirable to pro-' vide sheet metalterminals of copper or alloys of copper for convenience in makingoutside connections thereto and in some cases for supp rting the unitthereby. The terminals of copper or alloys of copper have the advantagesnot only of low resistance and a degree of flexibility and ease ofbending but also of enabling leads or connections to be soldered theretoreadily with the usual lead-tin solders.

However, if the terminal band or strip around the tube be made of copperin order to provide the sheet metal copper terminal, difficulties arisedue to its comparatively high coefficient of expansion. causing crazing01' the enamel and other dimculties as referred to in said prior Keblerpatent. It is therefore desirable to use a metal or alloy for theencircling or clamping elements which will have a lower coeiilcient ofexpansion than copper and of a proper value in order to overcome suchdifficulties. For this purpose. sheet iron or sheet steel may be used,as referred to in said Kebler patent, or preferably an alloy of about50% iron and about 50% nickel as referred to in the prior patent ofCharles J. Ganci. No. 2,179,212, .granted November '7, 1939. Such bandsor clamps also have the advantage of high tensile strength permittingthem to be made comparatively small and to be well covered by the.insulating coating; but they have the disadvantage of not enabling theuser tosolder outside connections thereto with the ordinary lead-tinsolder. Therefore it is highly desirable to combine with such a band asheet metal terminal of copper or of copper alloys which likewisesecures the other advantages of a copper terminal.

On'e object of the invention is to simplify the structure disclosed insaid priorKebler patent and to improve and simplify the method of makingthe-device. A further object is to insure. a good and permanentelectrical connection between the resistive conductor and the copperterminal.

Another object is to provide a structure which is applicable to varioussizes and forms of resistive with the clamping band;

thereof; and Fig. 8 is a side view of the complete 2 devices. Anotherobject is to provide an improved form of terminal structure and methodof making the same. Other objects and advantages will be understood fromthe follownig description and accompanying drawing which iluustrates apreferred embodiment of the invention as an illustrative example. I

Fig. 1 is a side view of a tubular resistive unit showing the assemblyof the parts before the insulating coating is applied; Fig. 2 is an endview thereof; Fig. 3 is a development of the clamping element or band;Fig. 4 is a fiace view of the sheet metal terminal or tab of copper orcopper alloy: Fig. 5 is an edge view thereof; Fig. 6 is a development ofthe copper terminal after being united Fig. '7 is an edge view device.

Referring to Fig. 1, a supporting tube l of porcelain or otherinsulating material is shown hav- 25 ments ing a resistive conductor 2wound thereon. Two end terminals are shown but if desired. any number ofintermediate terminals may be added to suit particular requirements. Theclamping eleor bands 3 of sheet iron. or steel, or of an alloy of ironand nickel are shown having a resistive conductor connected thereto.These bands have a desirable coeilicient of expansion lower than that ofthe sheet metal terminals 4 of cop- 80 per or copp i!- The developmgentof one of the bands is shown in Fig. 3 and is provided near one end witha notched portion la connected by a small neck 3b with the body of theband. This band is also provided with perforations c for permitting theinsulating coating to enter them and aid in firmly securing the band tothe insulating support 2. This clamping element may be readily stampedout of sheet metal.

The sheet metal copper terminal strip or tab 4 portion of the strip.

is shown in Figs. 4 and 5 and is of a form which may be readily cut orstamped from sheet metal. Near one end of the strip a small interior lipor tongue 4a is punched out from an interior midproiecting in adirection toand is'shown of rectangular lb may be stamped near ward thenear end form. A perforation the opposite end of the copper strip forconven-' ience in making connections to outside circuits.

Figs. 6 and '7 show the copper strip united with the clamping band andthis is accomplished by slipping the end of the copper strip on to theend of the band 8 so that the lip or tongue la passes over one side ofthe band, the end of the so copper strip engaging the opposite face ofthe 3 band. The Joined parts are then firmly compressed together attheir united portions forming a substantially flat strip throughout itslength with the terminal or tab 4 mechanically and firmly united withthe band I as shown in Fig. 7.

The combined strip is then bent substantially at right-angles along thedot and dash line shown in Fig. 6 and also near the opposite end of thestrip 3 so that when the bands are slipped over the ends of theinsulating tube l, the end portions come face to face, as shown in Fig.2 with the-copper terminal 4 supported between the ends of theencircling band and extending outwardly therefrom. The meeting portionsof the band are then spot welded so as to fuse the ends of theencircling band and the inner end of the terminal I together in a solidmetal portion. The terminal 4 is advantageouslv made of an alloy ofabout 6% nickel and balance of copper because such composition melts ata lower temperature than copper and improves the electrical connectionbetween the band and the terminal. It also permits the spot welding tobe accomplished at moderate temperatures and likewise the soldering ofthe outside connection to the terminal I is made easier than when aterminal of pure copper is used.

In connecting theresistive conductor 2 to the projecting portions 3a ofthe bands, these portions are first bent so as to extend outwardly fromthe bands. One end of the resistive conductor is then wound around andwithin the notched portions Ia and around the neck and then insuccessive turns around the tube, the remaining end of the conductorbeing similarly wound around the projecting portion and neck of theother end hand. These outwardly projecting portions are then dipped in asilver solder bath for brazing and permanently connecting the conductorto the encircling bands in accordance with the disclosures of my priorPatent No. 1,932,923, granted August 31, 1933. The projections Ia arethen bent inwardly close to the tube I after which the insulatingcoating 5, as

shown in Fig. 8, is applied, resulting in the finalproduct. It isapparent that the completed unit has a uniform and smooth externalsurface with no protruding portions or projections which are difficultto cover properly with the insulating coating. This coating ispreferably of vitreous enamel material and is matured in a furnace at acomparatively high temperature.

In making the device the encircling bands and copper terminals arereadily formed from sheet metal and are interlocked and mechanicallyfasicned together in a simple manner so as to be conveniently handled asa unit and mounted on the tube and then spot welded. Also, the brazedconnection between the resistive conductor and the encircling bands ispermanent and undisturbed by the firing in the enameling furnace andlikewise the spot welding of the opposed faces of the encircling bandand the intervening end of the copper terminal gives a fused connectionof solid metal between the copper terminal and the band which isunaflected during the firing operation. It follows that an excellent,permanent electrical connection is formed between the copper termlnalsand the conductor.

In making the unitary jterminal comprising the band and terminal tab, itis most readily accomplished by a counter-fed stamping interlocking andcompressing operation according to the following process. Strips for thebands and for the terminals are first prepared of the proper width andin long lengths. These are then fed through continuously operatingstamping machines in opposite directions toward each other. As thestamped and cut terminals are formed. they are passed toward each otherend to end so that the tongue formed on the copper alloy terminal passesover one end of the band and the other portion of the terminal passesover the opposite side of the end of the band. In this position theengaging end portions are then compressed flrmly together giving acombined unit interlocked and mechanically united by compression of theparts. The unit then may fall into a box or basket which serves as asupply of units for use in making the resistive devices as alreadydescribed. These terminal units are adapted for use in various types ofelectrical apparatus and may be made and sold as a unitary terminal forvarious uses.

Although a, preferred form of the invention has been described andpreferred methods of making, it will be understood that the same issubject to various modifications and adapted for use in various formsand types of devices according to particular conditions and requirementswithout departing from the scope of the invention.

I claim:

1. A resistive device comprising an insulating support, a resistiveconductor thereon, a terminal unit to which said conductor iselectrically con nected, said unit comprising a sheet metal stripembracing said support and having end portions facing each other, and asheet metal strip mainly of copper having an end portion located betweensaid facing end portions, one of said strips having an interior tongueextending from the body thereof and extending over the end and engaginga face of one of the end portions opposite from the face thereof engagedby said last named strip.

2. A resistive device comprising an insulating support, a resistiveconductor thereon, a terminal unit to which said conductor iselectrically connected, said unit comprising a sheet metal stripembracing said support and having end portions facing each other, and asheet metal terminal mainly of copper having an end portion locatedbetween said facing end portions, said terminal having an interiortongue extending from the body thereof engaging a face of one 01' saidend portions opposite from the face thereof engaged by said terminal.

3. A resistive device comprising an insulating support, a resistiveconductor thereon, a terminal unit to which said conductor iselectrically connected, said unit comprising a sheet metal stripembracing said support and having end portions facing each other, and asheet metal terminal mainly of copper having an end portion locatedbetween said facing end portions, said terminal having an interiortongue extending from the body thereof and extending over the end andenging a face of one of said end portions opposite flrom the facethereof engaged by said termina 4. A resistive device comprising aninsulating support, a resistive conductor thereon, a terminal unit towhich said conductor is electrically connected, said unit comprising asheet metal strip embracing said support and having end portions facingeach other, and a sheet metal terminal mainly of copper and nickelhaving an end portion located between said facing end portions, saidterminal having an interior tongue extending from the body thereofensuing a face of one of said end portions opposite from the facethereofengaged by said terminal, said meeting end portions being spot welded toform a solid joint.

5. The method of making a resistive device comprising forming strips ofsheet metal, one of said strips being of material having high tensilestrength and the other of said strips being mainly of copper, forming aninterior protruding tongue on one of said strips, joining said stripsend to end with the faces of their end portions in con tact and saidtongue embracing the face of the other strip opposite from thecontacting face portions, compressing the engaged portions to form amechanically joinedunit, embracing an insulating support by said unitand bringing one end of said unit to face said compressed portions,welding said last named end to said compressed portions, mounting a,resistive conductor on said support, and electrically connecting saidconductor to said unit.

6. A terminal unit comprising two strips of different material joinedend to end with the faces of their end portions in contact, and one ofsaid strips havingan interior tongue portion projecting therefrom andembracing the face of the other strip opposite from the contacting faceportions, said joined portions being compressed to form a mechanicalconnection between the ends of said strips.

7. A terminal unit comprising two stripsof dif ferent material joinedend to end with the faces of their end portions in contact, and one ofsaid strips having an interior tongue portion projecting therefrom andextending over the end of the other strip and embracing the face of theother mainly of copperand nickel joined end to end 1 with the faces oftheir end portions in contact, and one of said strips having an interiorportion embracing the face of the other strip opposite from thecontacting face portions, said joined portions being compressed to forma mechanical connection between the ends of said strips.

9. The method of making a terminal unit com prising forming two stripsof different material, joining said strips end to end with the faces oftheir end portions in contact, and with an interior tongueportionprojecting from one of said strips embracing the face of the other stripopposite from the contacting face portions, and compressing said joinedportions to form a mechanical connection between said strips.

10. The method of making a terminal unit comprising forming two stripsof different material with one-of said strips having an interior tongueportion projecting therefrom, feeding said strips end to end toward eachother to bring the faces of their end portions in contact and with saidtongue extending over the end and embracing the face of the other stripopposite from the contacting face portions, and compressing the engagedportions to form a mechanical connection between said strips.

. FREDERIC H. BUILINGER.

